During the offshore installation of the mother case, “An Integrally Equipped Heavy Draught Floating Type Oil Production Platform with Unconditional Stability”, a column with small cross section is gradually transferred to a lower level through the central pore canal of a column with large cross section in a controlled state, and then columns with small cross section and large cross section are permanently connected. The adopted connection manner is as follows: using a crane to place a hydraulic forging connection equipment through the central pore canal at the junction of columns with small cross section and large cross section for hydraulic forging, and plastically deforming an outer wall plate at the junction of columns with small cross section and large cross section by a hydraulic pressure, and then squeezing the outer wall plate into a groove of a chopping board connection structure at the junction of a lower portion of the column with large cross section so that structures of the two portions are coupled as a whole by the full strength.
In the mother case, the offshore installation and connection operation is the key operation condition, which mainly has the following technical challenges and risks: (1) during installation, columns with large cross section and small cross sections are in the state of motion, wherein the operating space is small, and in addition to the limitation of environmental conditions, the installation time is restricted; (2) after the platform is in place, the connection joint is one of the areas subjected to the largest external load in the entire platform, which bears the combined effect of a bending moment and a shear force, and also has challenges about how to ensure the strength and fatigue of a joint.
Considering the technical difficulty of the connection joint, although a hydraulic expanding tube provided by the mother case is feasible, there exists the following problems in operation: (1) in the mother case, when a structural plastic deformation is made by a hydraulic pressure, the accuracy control requirement for relative positions of the grooves of columns with large cross section and small cross sections is high, but at this time columns with large cross section and small cross sections are in the state of motion, having a vertical movement, a horizontal movement and a rotation, so there exists great difficulty to ensure the relative positions of the both unchanged; (2) it is difficult for the prior art of the hydraulic expanding tube to adapt to connections of columns with a large diameter, which brings a great limitation to the design of columns of the platform; (3) the original connection solution makes the local structure (e.g., the local area of an inner wall of the column with large cross section and an outer wall of the column with small cross section) of the platform plastically deformed, and columns with large cross section and small cross sections are connected as a whole by plastic deformation, wherein the process is not reversible, and once a problem arises in operation, it will have a great impact on the platform structure, so there exists technical and safety risks in the solution.